Transcript for North Koreans Chant 'Death to US Imperialists' at Mass Rally

now to a new and even more provok tiff movement by north korea. Even more uncertainty about the young, untested leader, kim jong-un. Abc's bob woodruff, who has traveled inside north korea, has the news tonight. Reporter: A rally 100,000 strong chanting death to to the u.S. Imperialist. Their leader, kim jong-un, seated, with a war plan. Look closely, and the words appear to say "strategic forces plan to hit the u.S. " and a new propaganda video showing the north striking an an american bomber, released just hours after the u.S. Flew the stealth b-2 over the peninsula in a show of force. There are concerns that the tensions are racheting up. All anyone needs to do is light a match and it could set off a second korean war and that's the real danger here, because that would be catastrophic. Reporter: What's so worrying is that we know so little about the new, young leader. We were there two and a half years ago when the world first saw him. He seems more westernized enjoying mickey mouse and american basketball. Even meeting with former nba star dennis rodman. But he is also acting more aggressively than some analysts hoped, launching rockets into space and building a nuclear arsenal. The north's threats are red hot. If you were going to rate this from one to ten, ten, the most dangerous, what number would you put it? I would say we're either at eight or nine at the moment. Reporter: While south korean media reported the north may be preparing for another missile test, the range is limited. But the north can clearly strike throughout asia, including our allies, south korea and japan. Allies we are committed to defending. Now, one other issue is that there is just very little communication between the two koreas and we've reported that north core korea has cut all the last military hotlines with south korea and analysts don't know if all the leader's propaganda pictures are real threats to us or simply political theater to show his power to his own people.

This transcript has been automatically generated and may not be 100% accurate.

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